The IPCC SRES (Nakic´enovic´ et al., 2000) developed 40 future
scenarios that are characterised by distinctly different levels of population,
economic, and technological development. Six of these scenarios were identified
as illustrative scenarios and these were used for the analyses presented in
this chapter. The SRES scenarios define only the changes in anthropogenic emissions
and not the concurrent changes in natural emissions due either to direct human
activities such as land-use change or to the indirect impacts of climate change.
The annual anthropogenic emissions for all greenhouse gases, NOx,
CO, VOC and SO2 (sulphur dioxide) are given in the SRES for the preliminary
marker scenarios (Nakic´enovic´ et al., 2000, Appendix VI) and the
final marker/illustrative scenarios (Nakic´enovic´ et al., 2000,
Appendix VII). Much of these data is also tabulated in Appendix
II to this report. There are insufficient data in the published SRES (Nakic´enovic´
et al., 2000) to break down the individual contributions to HFCs, PFCs, and
SF6, but these emissions were supplied by Lead Authors of the SRES
(available at sres.ciesin.org) and are
also reproduced in this Appendix. The geographic distribution of emissions of
the short-lived compounds – NOx, CO, VOC, and SO2
is an important factor in their greenhouse forcing, and the preliminary
gridded emissions were likewise supplied by the SRES Lead Authors (Tom Kram
and Steven Smith, December 1998) and used in the OxComp model studies. A synopsis
of the regional shift in CO and NOx emissions projected by 2100 is
given in Tables 4.6 and 4.8.

This chapter evaluates the SRES emissions from year 2000 to year 2100 in terms
of their impact on the abundances of non-CO2 greenhouse gases. A
new feature of this report, i.e., use of NOx, CO and VOC emissions
to project changes in tropospheric O3 and OH, represents a significant
advance over the level-of-science in the SAR. The original four preliminary
marker scenarios (December 1998) are included here because they have been used
in preliminary model studies for the TAR and are designated A1p, A2p, B1p, B2p.
In January 1999, these emissions were converted into greenhouse gas abundances
using the level-of-science and methodology in the SAR, and the radiative forcings
from these greenhouse gas abundances were used in this report for some climate
model simulations.

The recently approved six marker/illustrative scenarios (March 2000) are also
evaluated and are designated A1B-AIM, A1T-MESSAGE, A1FI-MiniCAM, A2-ASF, B1-IMAGE,
B2-MESSAGE (hereafter abbreviated as A1B, A1T, A1FI, A2, B1, B2). For comparison
with the previous assessment, we also evaluate the IPCC emissions scenario IS92a
used in the SAR; for the full range of IS92 scenarios, see the SAR. An agreed-upon
property of all SRES scenarios is that there is no intervention to reduce greenhouse
gases; but, in contrast, regional controls on SO2 emissions across
the illustrative SRES scenarios lead to emissions in the last two decades of
the century that are well below those of 1990 levels. There appear to be few
controls on NOx, CO and VOC emissions across all scenarios; however,
the large increases in surface O3 abundances implied by these results
may be inconsistent with the SRES storylines that underpin the emissions scenarios.
As understanding of the relationship between emissions and tropospheric O3
abundances improves, particularly on regional scales, more consistent emissions
scenarios can be developed. The SRES scenarios project substantial emissions
of HFC-134a as in IS92a, but only half as much HFC-125, and no emissions of
HFC-152a. The SRES emissions scenarios do include a much larger suite of HFCs
plus SF6 and PFCs, which are not included in IS92a. The emissions
of greenhouse gases under the Montreal Protocol and its Amendments (CFCs, HCFCs,
halons) have been evaluated in WMO (Madronich and Velders, 1999). This report
adopts the single WMO baseline Montreal Protocol Scenario A1 (no relation to
SRES A1) for emissions and concentrations of these gases, while the SRES adopted
a similar WMO Scenario A3 (maximum production); however, the differences between
scenarios in terms of climate forcing is inconsequential. The resulting abundances
of greenhouse gases are given in Appendix II and discussed
in Section 4.4.5.